Federal housing chief Ben Carson visited a New York City public housing development for the first time Tuesday, amid City Hall's concerns that the federal government could take over the city's public housing agency.

A slew of NYPD officers stood guard outside the Queensbridge Houses on Tuesday morning for a surprise special visitor. Around 10:30 a.m., two black cars pulled up. Out stepped the secretary for the U.S. Department of Housing and Urban Development (HUD).

Our cameras were kept outside, but Carson's agency tweeted out photos. He checked out a boiler and one apartment. His visit was about a half-hour, and he did not take any questions from us. It was the first time Carson, who has been the head of HUD for about two years, has visited the largest housing system in the United States.

A federal takeover is on the table, something the regional director of the federal housing department supports.

"Well, I hope Secretary Carson sees firsthand the horrid conditions that these residents have been forced to endure for far too long," said Lynne Patton, the regional administrator for HUD.

• Lynne Patton Has Called for New Leadership at NYCHA. Has That Changed After Ben Carson's Visit?

Carson sent a letter to NYCHA on Friday threatening to put the agency in "substantial default," which would be the first step to taking over the struggling agency. It could lead to something called a receivership.

Carson demanded NYCHA come up with a plan to address all of his concerns by January 31. At the same time, the city must submit a plan in federal court, part of settlement talks with the U.S. Attorney's office.

Immediately after his visit to Queensbridge Houses, Carson went to Manhattan. He sat down with Mayor Bill de Blasio for about an hour.

After that meeting, we asked the mayor whether the prospect of receivership, something de Blasio opposes, came up. De Blasio said the two of them were on the same page.

"I think there was a broad agreement that we will do all together to avert it. That both HUD and the city of New York believe there is a better way, and that better way is come to a settlement," de Blasio said.

There's a lot of uncertainty surrounding the future of the city's public housing system, and it looks like we won't have any real answers until the end of January.